System for inductive wireless power transfer for portable devices

Abstract

In one embodiment a wireless power transfer system comprises a transmitter including a power source configured to generate a time-varying current, a first coil configured to receive the first time-varying current from the power source, wherein the time-varying current flows in the first coil in a first direction, a second coil coupled to the first coil in such a way that the time-varying current flows in the second coil in a second direction, wherein the first direction is opposite from the second direction, and an underlying magnetic layer configured to magnetically couple the first coil with the second coil, and a wireless power receiver, a ferrite core and a receiver coil that share a longitudinal axis, and a receive circuit coupled to the receiver coil configured to convert a time varying current induced in the receiver coil into a voltage.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims the benefit of U.S. Provisional Patent Application No. 62 / 266,128, entitled “Wireless Power Transfer for Wearables,” filed on Dec. 11, 2015. This application is also related to U.S. patent application Ser. No. 15 / 082,533, entitled “Wireless Power Transfer Using Multiple Coil Arrays,” filed on Mar. 28, 2016. The subject matters of the related applications are hereby incorporated by reference in their entirety.FIELD OF THE INVENTION[0002]This invention relates generally to inductive wireless power transfer and more specifically to a system for wireless power transfer for portable devices.BACKGROUND[0003]Electronic devices typically require a connected (wired) power source to operate, for example, battery power or a wired connection to a direct current (“DC”) or alternating current (“AC”) power source. Similarly, rechargeable battery-powered electronic devices are typically charged using a wired power-supply that conn...

AI Technical Summary

Benefits of technology

Enhances power transfer efficiency by reducing magnetic reluctance and enabling charging of non-flat devices and smartphones in vehicles, improving the usability of wireless power transfer technology for a wider range of consumer and industrial devices.

Problems solved by technology

The limitation of these devices is the need to directly connect the device to a power source using wires.

The problem with near-field WPT technology is that typically only 5 Watts of power can be transferred over the short distance of 2 to 5 millimeters between a power source and an electronic device, though there are ongoing efforts to increase the power.

Magnetic flux lines tend to repel if they are in the same direction, which causes the flux lines to radiate through the air for great distances.

If the transmitter coils are placed on separate magnetic layers, an air gap exists between the magnetic layers resulting in an even weaker generated magnetic field as the air gap further increases the reluctance between the transmitter coils.

This makes it difficult to implement wireless power transfer for devices that are not perfectly flat or do not have a large enough area for embedding a typical receiver coil (e.g., Android® wearable devices, Apple® watch, Fitbit® fitness tracker, etc.).

The limitations of WPT also affect smartphones if the charging surface with the transmitter coil is not large enough to allow the smartphone device to sit flat on the surface (e.g., in vehicles, which typically do not have a large enough flat surface to accommodate a smartphone device).

Thus, the current state of WPT technology is not suitable for many consumer or small industrial devices.

Images